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A large area plasma source based on 12 multi-dipolar ECR plasma cells arranged in a 3 × 4 matrix configuration was built and optimized for silicon etching by negative ions. The density ratio of negative ions to electrons has exceeded 300 in Ar/SF6 gas mixture when a magnetic filter was used to reduce the electron temperature to about 1.2 eV. Mass spectrometry and electrostatic probe were used for plasma diagnostics. The new source is free of density jumps and instabilities and shows a very good stability for plasma potential, and the dominant negative ion species is F-. The magnetic field in plasma volume is negligible and there is no contamination by filaments. The etching rate by negative ions measured in Ar/SF6/O2 mixtures was almost similar with that by positive ions reaching 700 nm/min. [ABSTRACT FROM AUTHOR]